Thin alloy films of metallic components on suitable substrates are used as magnetic storage media, switching elements or as sensors, in the case of storage applications, critical importance being placed on the orientation of the magnetic moments relative to the layer surface.
The bit storage size can be reduced by reducing the magnetic volume in which the information is stored. However, such a reduction inevitably results in a loss of thermal stability of the stored information (superparamagnetic limit, thermal excitation of remagnetization processes above a characteristic temperature), thereby limiting the storage density that is attainable at the present time.
By selecting appropriate classes of material and by employing patterning methods, it is possible to significantly increase the storage density. This requires using systems which exhibit a perpendicular magnetocrystalline anisotropy. At the present time, ternary material combinations, such as Co—Cr—Pt, which necessitate costly production methods to introduce the same, as well as a thermal treatment, are used for this purpose.
Yong Lei and Wai-Kin Chim, Shape and Size Control of Regularly Arrayed Nanodots Fabricated Using Ultrathin Alumina Masks, Chem. Mater. 2005, 17, pp. 580-585, describe the production of highly ordered semiconductor and metallic structures from nanoparticles having controllable sizes and shapes. These structures are deposited via nanoporous membranes of Al2O3, which are also described as ultrathin alumina masks or UTAMs, onto Si and Si/SiO2 substrates. The size and shape of the structures can be controlled by the aspect ratio of the apertures of the traversing pores of these membranes, as well as by the quantity of material. These masks can also be used at higher temperatures for epitaxial growth. It has been possible up until now to employ this method to fabricate ordered structures of semiconductive nanoparticles having sizes of up to 20 nm.
In Magnetic Properties of Ferromagnetic Nanowires Embedded in Nanoporous Alumina Membranes, Journal of Magnetism and Magnetic Materials 249 (2002), pp. 241-245, M. Kröll, W. J. Blau, D. Grandjean, R. E. Benfield, F. Luis, P. M. Paulus and L. J. de Jongh describe producing iron, nickel and cobalt nanowires from Al2O3 using nanoporous membranes. These nanowires can be adjusted in diameter (5-250 nm) and length (up to a few hundred micrometers).
In Preparation of Fe/Pt Films with Perpendicular Magnetic Anisotropy, Hyperfine Interactions (2005) 160, pp. 157-163, S. Kavita, V. R. Reddy, A. Gupta and M. Gupta describe the structures and magnetic properties of L10 ordered, thin equiatomic FePt films, which were produced by ion beam sputtering and subsequent annealing.
US 2002/0158342 A1 describes an element which includes a substrate onto which a multiplicity of nanocylinders are deposited, each nanocylinder having superposed layers alternately composed of atoms of a magnetic element and of a non-magnetic element. The element is fabricated using a diblock copolymer, upon which a metal layer is at least partially deposited, which, following orientation and removal of one component of the diblock copolymer, forms nanocylinders.
However, selected binary alloy systems, such as the Fe—Pt, Fe—Au or Co—Pt system, can likewise exhibit the desired properties. In the case of material synthesis preferably carried out by vapor deposition processes, kinetic inhibition prevents the ordering of the desired L10 phase having perpendicular magnetocrystalline anisotropy from being effectively controlled. Rather, the system crystallizes at room temperature in the disordered fcc phase, accompanied by random filling of the lattice sites. However, the desired orientation can be controlled by applying suitable vapor deposition parameters. As a result, material combinations can be artificially produced which do not provide a thermodynamically stable configuration for the L10 order. An example of this is the deposition of Fe and Au in monolayers.